Async support

[LEXUGE]

Currently, the niffler only supports Write and Read defined in std. However, AsyncRead or AsyncWrite like those in tokio are also demanded for operating large files or processing files with high disk latency.

[natir]

At the moment AsyncRead or AsyncWrite trait is define by async backend like futures or tokio.
Manage each async backend, could require many code.
We also need compression backend support AsyncRead and AsyncWrite, for example it's not the case for flate2, but async-compression could be nice.

I agree with you, it could be nice to have this Async interface but it's maybe need many change in niffler. So it could take time.